Referring to FIG. 1, there is shown a motorized roller tube system 10 having a prior drive assembly 12. The motorized roller tube system 10 includes a rotatably supported roller tube 14 and a flexible member 16, such as a window shade fabric, windingly received by the roller tube 14. The flexible member 16 is typically engaged to the roller tube 14 by securing an end portion of the flexible member 16-to the roller tube 14. There are a variety of well-known means for securing the flexible member 16 to the roller tube 14 including, for example, the use of double-sided tape, or by a clip member received over an end portion of the flexible member 16 in a locking channel provided on the exterior of the roller tube 14. The roller tube 14 is driven in opposite rotational directions by the drive assembly 12 for winding and unwinding the flexible member 16 with respect to the roller tube 14. The prior drive assembly 12 includes an elongated housing 18 and a puck 20 located adjacent an end of the housing 18. The puck 20 engages an inner surface of the roller tube 14 to drive the roller tube 14 as the puck is rotated by the drive assembly 12.
The prior roller tube drive assembly 12 includes a motor 22 and gear assembly 24 located within an interior of the housing 18 and connected to the puck 20. The motor 22 and gear assembly 24 are shown in FIG. 2 removed from housing 18. The motor 22 of prior drive assembly 12 is a DC motor. Referring again to FIG. 1, the drive assembly 12 is received within the interior of the roller tube 14. For this reason, this type of roller tube drive assembly is referred to as an “internal” drive assembly. Other known motorized roller tube systems include drive assemblies that are located externally of the roller tube.
The motor 22 includes an output shaft 23 that is rotated by the motor at a rotational speed referred to herein as the “motor speed”. The prior drive assembly 12 operates the motor at a motor speed of approximately 2000 rpm. The gear assembly 24, which is connected to the output shaft of the motor 22, reduces rotational speed from the relatively fast speed of 2000 rpm input from motor 22 to a relatively slow output rotational speed of approximately 27 rpm for roller tube 14. The gear assembly 24 of the prior drive assembly 12, therefore, has a gear ratio of approximately 74:1 (i.e., 2000/27).
The torque capability of a motor varies depending on the motor speed. Therefore, the motor of any motorized roller tube system must provide a torque capability at the operating motor speed that is sufficient to wind the flexible member 16 onto the roller tube 14. Referring to FIG. 3, the performance characteristics for motor 22 of prior drive assembly 12 are shown graphically. Graphs of this type are referred to as “motor curves”. The relationship between motor speed (shown on the Y-axis) and motor torque capability (shown on the X-axis) is represented by line 26. As shown, the maximum motor speed for motor 22 is approximately 3150 rpm and the maximum motor torque capability is approximately 280 m-Nm. As also shown, the motor torque capability for DC motor 22 varies linearly throughout the entire range of motor speeds. In other words, the motor will provide increasing torque capability with decreasing motor speed even at very slow speeds approaching zero. It should be understood the motor torque values on speed/torque line 26 of FIG. 3 represent capability rather than fixed values of operating motor torque. In other words, the motor 22 is capable of operating at a given motor speed at any torque between zero (i.e., an unloaded condition) and the value represented on the speed/torque line 26. At the operating speed of 2000 rpm, the torque capability of motor 22 is approximately 99 m-Nm.
As shown in FIG. 3 by curve 28, the efficiency of motor 22 also varies depending on the motor speed. The efficiency, which is shown on the Y-axis with motor speed, is determined by reading vertically from the speed/torque line 26 to the efficiency curve 28. Thus, at the operating motor speed of 2000 rpm, the motor 22 of prior drive assembly 12 has an efficiency of approximately 25 percent. As shown, the motor efficiency of 25 percent is the peak efficiency for motor 22. The motor speed associated with peak efficiency is referred to herein as the peak efficiency motor speed. The peak efficiency motor speed represents approximately 65 percent of the maximum motor speed (i.e., 2000/3100).
Although the particular values of motor speed, torque capability, and efficiency will vary for different DC motors, there are certain characteristics that are shared by all DC motors. Firstly, motor speed and motor torque capability will vary linearly, and inversely, throughout the entire range of motor speeds including very low speeds approaching zero. Secondly, motor efficiency will generally reach peak efficiency under light-duty conditions (i.e., relatively low torque capability at a motor speed greater than 50 percent of maximum motor speed). Prior drive assemblies include motors configured and operated by the drive assembly under light-duty conditions near the peak efficiency motor speed. As described below in greater detail, operation of the motors under such relatively light-duty conditions is in accordance with motor manufacturer recommended operation of the motor.
The gear assemblies of known roller tube drive assemblies include planetary spur gears. Planetary spur gears are desirably economical in construction and provide efficient transmission compared to other types of gears. Spur gears, however, tend to be noisy in operation compared to other gear types because of sound generated as peripheral teeth contact each other. This contact sound associated with meshing teeth is sometimes referred to as “gear slapping” and increases as the rotational speed of the meshing gears is increased. Known gear assemblies also include gear stages having helical gears. Helical gears include elongated spiral flights that constantly engage with flights of other helical gears. The constant engagement of the flights eliminates the slapping noises associated with contact between the teeth of spur gears. Helical gears, however, tend to be less economical and less efficient than spur gears.
The gear assembly 24 of prior drive assembly 12 includes three gear stages 30, 32, 34. The gear assembly 24 is a hybrid gear system and includes a first stage 30 having helical gears and second and third stages 32, 34 each having planetary spur gears. The first gear stage 30 is located closest to the motor 22. The gears of stage 30, therefore, are rotated at the relatively fast motor speed of 2000 rpm. The rotational speed in the second and third stages 32, 34, however, is stepped down from the 2000 rpm motor speed. Thus, the hybrid construction of prior drive assembly 12 represents a trade-off in which quieter, less efficient, more expensive helical gears are used in the relatively fast first stage 30, while efficient, less expensive, but noisier, planetary spur gears are used in the relatively slower second and third stages 32, 34.
Prior motorized roller tube systems include systems providing for variable-speed control of a drive assembly motor. The variable-speed control feature is used in prior systems to provide for movement of the flexible member (known as “linear speed” or “fabric speed”) that is substantially constant. The variable motor speed adjusts the tube rotational speed to account for variation in the effective winding radius associated with the formation of winding layers as the flexible member is wound onto the roller tube. If the roller tube were to be rotated at a constant rotational speed, the fabric speed would change as the effective radius changed. Prior motorized roller tube systems control the motor speed to slow down the motor speed as the flexible member is wound onto the roller tube for substantially constant fabric speed. The prior motorized roller tube systems, however, do not provide for multiple modes of operation in which the fabric speed in each mode of operation is different from the fabric speed in the other modes of operation.